1. Field of the Invention
The invention relates to a device for generating ozone from oxygen or gas containing oxygen by silent electric discharge in a discharge space through which the gas flows and which is essentially formed by an outer tube of dielectric material and an internal electrode, arranged inside the said tube, and an external electrode, surrounding the outer tube.
With this preamble, the invention makes reference to a prior art such as arises for example from German Offenlegungsschrift 3,422,989 or Swiss Patent Application 3383/88-8 of Sept. 9, 1988 by the applicant.
2. Discussion of Background
The increasing use of ozone for chemical and physical purposes has resulted in the ozone tube developed by Siemens having been decisively improved recently in technical and commercial respects. For instance, it is proposed in U.S. Pat. No. 2,811,217 to increase the ozone yield by certain characteristic variables of the ozonizer (frequency of the feed voltage, dielectric constant of the dielectric material, amplitude of the feed voltage, thickness of the dielectric layer and size of the discharge gap) having to satisfy certain laws.
In other publications, special cooling measures are proposed for the same purpose, in order to increase the ozone yield, for example, apart from the liquid cooling of the external electrode, the internal cooling of the high-voltage electrode with gas or liquid in German Offenlegungsschrift 2,357,392, or the intermediate cooling of the charge gas enriched with ozone in the case of ozonizers arranged in series in German Offenlegungsschrift 2,436,914.
The state of the art today are discharge gap widths around 1 mm. A further reduction in the gap widths is confronted by the geometrical tolerances of the metal and dielectric tubes used. In particular in the case of relatively large tube lengths, a further reduction in the gap widths is limited by the ever-present flexures of the dielectric and metal tubes.
For the purpose of increasing and making more uniform the intensities of the field strengths, it is proposed in German Offenlegungsschrift 3,422,989 to design the internal electrode as a solid metallic rod. Due to its small diameter in comparison with a tube, the field strength at its surface is great. Since the diameter of the external electrode, designed as a metal tube, is correspondingly reduced and thin material thicknesses are used, a flexible structure is obtained. The distance between external and internal electrode and dielectric can be maintained very accurately over the entire length. As a result, a uniform intensity of the field strength, good cooling possibilities, compact design and high output are obtained.
However, this known ozonizer is comparatively complex.
In the Swiss Patent Application cited at the beginning, on the other hand, a completely different approach is presented: a homogenous discharge gap is dispensed with entirely, instead taking care to ensure that the heat generated by the (inhomogenous) discharges is dissipated in as direct a way as possible. For this purpose, thin glass tubes provided with internal electrodes are packed tightly between two cooled metallic plates and a discharge struck externally between the glass tubes and the metallic plates. In some embodiments, a discharge is additionally struck inside the glass tubes.